Sunday, July 17, 2011

Chytrid Fungus Killing Frog Populations

Chytrid fungus is a zoosporic fungus, Batrachochytrium dendrobatidis. Once it infects a host, it will feed off the host for a few days. Then it will asexually reproduce, forming a zoospore. This zoospore is released into the surrounding moist environment. It will move through the water, but it is most often through direct contact that it is spread. It moves by use of a flagellum. It once again infects a host, and the cycle begins again. This process takes up to two weeks. Some of the zoospores will stay embedded in the skin, and re-infect the host. It prefers cool, moist environments, and it infects amphibians, mostly frogs. It can live in aqueous environments for months, but cannot live but a few hours in warm, dry conditions.

Once it has infected a frog, it feeds off the keratin in the frog's skin. It makes the skin thick, which affects the frog's ability to uptake water and electrolytes through its skin. This can cause complications in the frog's heart due to a lack of these important electrolytes. The frog also uses its skin for respiration, so an infection will make it difficult for the frog to "breathe." in come cases, it can also affect the nervous system. A frog that is infected with the chytrid fungus will most likely present with discolored skin, lethargy, not protecting itself from the environment, peeling of the skin, and its legs will be splayed away from its body instead of underneath. (Frog Chytrid Fungus, 2011) Some instances of seizures have also been noted.

As stated above, the chytrid fungus is spread through direct contact or through water that is infected. Scientists have realized that the zoospores can be relocated through transfer on wet clothing and footwear. Moving frogs and amphibians that are infected to new locations where the fungus is not present can also aid in its spread. Sometimes birds and insects that move between different environments can also transfer the fungus. This fungus was first discovered in amphibians in Australia in the early 1990's. It is now widespread around the world. (Briggs, Knapp, & Vrendenburg, 2010)

One thing that scientists are studying is the effect of climate on the chytrid fungus. It does not thrive in temperatures above 82 degrees F, or below 50 degrees, although it prefers temperatures between 63 degrees and 77 degrees F. This is one reason it is abundant in the tropical rain forests. Cool days and warm nights provide a perfect atmosphere for the fungus to thrive. And with global warming, it continues to flourish. As the earth's temperature increases, it causes more cloud formation in the rain forest. This cloud cover causes the cooler temperatures in the day and warmer ones at night, creating the perfect environment for the fungus to grow. (Altwood, 2009)

The problem with this fungus is that frog species are now becoming extinct. There are approximately 6,200 species of frogs worldwide, and one third of these are endangered or extinct. This fungus is playing a large role in this. (Borrell, 2009) The Amphibian Conservation Summit reports that this fungus is the "worst infectious disease ever recorded among vertebrates in terms of the number of species impacted, and its propensity to drive them to extinction." (Briggs, Knapp, & Vrendenburg, 2010)

There are studies being done to determine a fix for this problem. Some researchers see using the natural bacteria found of the skin of frogs, which may block the fungus. Another way is to catch and treat the infected frogs. But finding all the infected frogs and preventing them from becoming reinfected poses a problem. (University of Zurich, 2011) But finding a way to stop the spread of this fungus has not been found.